If the allocation fails in DO_TEST_FLUSH_PROLOGUE, then 'mgr == NULL',
but the code continues on - which won't be good. So modify the macro
to cause an immediate failure and jump to a cleanup label.
Found by Coverity as FORWARD_NULL event.
This module will be used to track:
<domain, mac address list>
pairs. It will be important to know these mappings without
libvirt connection (that is from a JSON file), because NSS
module will use those to provide better host name translation.
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>